Yup. In normal light, you can't really see a clear difference between parts of the scalp with high density and parts with low density. However, the stronger the light, the more obvious it becomes.
Also, the top of your head is generally much more exposed to the light then the sides and the back. Try standing directly under a light source and look at your scalp in a mirror while you lay your head on a shoulder. You'll notice that because the side is now much more exposed to the light instead of the top, it'll look thinner while your top will look thicker.